<div class="panel-heading">
    <h4 class="widget-title">文章分类</h4>
</div>
<ul class="list-group">
    <li class="list-group-item" ng-repeat="(category, posts) in categories">
        <div class="widget-list-item">
            <i class="fa fa-caret-right"></i>
            <a ng-href="#/category/{{category}}">{{category}} ({{posts.length}})</a>
        </div>
    </li>
</ul>